Who knew biking in place could be such a competitive business? SoulCycle and Flywheel have their celebrity fans, but it's Peloton that's taking spinning to the masses and developing a cult following. This New York City-based start-up sells $2,000 spinning bikes and $39-a-month live-streamed classes that can be displayed on the bike's screen. There are more than 4,000 different on-demand classes and 14 daily live-streamed sessions. The bikes may seem pricey, but investors still feel there are enough customers out there who want to get a great workout in the privacy of their home (or who don't live near a great spin studio). It raised almost $445 million from Wellington Management, Fidelity Investments, Kleiner Perkins and GGV Capital, to name a few. The company has been valued at $1.4 billion.

Peloton — the name refers to the main group of riders in a race — was started in 2012 by John Foley, Tom Cortese, Yony Feng, Graham Stanton and Hisao Kushi. (Foley is CEO; the others all have roles in the company.) The group loved cycling but could never find classes that fit in with their schedules. Working out at home never seemed to be tough enough. That's when they decided to create a next-generation indoor bike and streamed classes that would simulate a cycle studio experience.

Earlier this year the company introduced the Peloton Tread, which brings the same intense in-home workout experience to treadmills. They're a bit pricier than the bikes — $3,995 — but will also come with their own $39-a-month subscription plan for streamed workouts. The treadmills will begin shipping in the fall but can be ordered now.